The principal aim of ST Award is to describe the impact of coexistent medic l and psychiatric disorders - comorbidity - on geriatric inpatients' length o hospital stay and cost. Epidemiological studies report 30-60% of medical inpatients have a concurrent psychiatric disorder. Psychiatric comorbidity patients have increased medical morbidity, mortality rates, and utilization of medical resources. Medical, psychiatric and psychosocial data will be prospectively collected from a probability sample of 620 medical/surgical admissions who are 65 yea s or older to a university hospital. Each patient will be evaluated with a structured diagnostic interview (SCID-NP) to establish the diagnosis of adjustment, anxiety, depressive, psychotic and substance use disorders, and delirium and dementia, using DSM-III-R criteria at admission and discharge. Both the severity of medical and psychiatric illnesses, and physical activi y level will be rated using validated measures. Each patient's length of stay total cost per stay, and daily cost will be ascertained using chart audit a d computerized cost accounting databases. The study will determine the contribution of psychiatric comorbidity to the prolongation of hospital stay and increased cost. The incremental cost of t e presence of psychiatric comorbidity on the following services will also be examined: nursing care, diagnostic and therapeutic radiology, pharmacy, therapies (eg. rehabilitation), and laboratory tests. Statistical analyses will include determination of differences in stay and cost between the comorbidity and non-comorbidity inpatients. Multivariate regression models such as life table analyses will be tested to predict the length Of hospita stay of comorbidity inpatients. Ultimately, this patient level economic microanalysis may elucidate the contribution of psychiatric comorbidity to the variance in length of hospit l stay and cost generated by geriatric inpatients, and provide baseline data to design studies of the utility and cost-effectiveness of psychiatric heal h services interventions in the medically ill. This study may increase physicians' awareness of psychiatric disorders in the hospitalized elderly, and potentially induce insurors to assume the cost of early psychiatric intervention in the medically ill.